1. Field of the Invention
The present invention relates to a device for operating a parking brake for vehicles such as automobiles and, more particularly, a device for operating a parking brake of a pivotable lever type.
2. Description of the Prior Art
A device for operating a parking brake of the pivotable lever type generally comprises a lever arranged to be pivotable around a pivot axis and connected with one end of a cable for actuating the parking brake, a ratchet element having ratchet teeth arranged along an arc centered at said pivot axis, a pawl pivotably supported by said lever and adapted to selectively engage said ratchet teeth in a manner to effect a one-way lock of the pivotable movement of said lever, a spring which resiliently drives said pawl into engagement with said ratchet teeth, and a release element for biasing said pawl to be out of engagement with said ratchet teeth, wherein a pivotable movement of the lever causes a stretching of said cable thereby actuating the parking brake. In this conventional device, when the lever is pivotally moved in the brake fastening direction, the pawl moves loosely over the ratchet teeth thereby allowing the lever to move pivotally in said direction, whereas when the lever is going to be pivotally moved in the opposite direction of releasing the brake, the pawl engages one of said ratchet teeth and locks the pivotable movement of said lever.
In the conventional device, therefore, the pawl can engage the ratchet teeth any time when the lever is going to be pivotally moved in the direction of releasing the brake regardless of whether or not the lever is pivotally moved to a position for applying a sufficient tensile force to the cable for ensuring the operation of the parking brake. Consequently, the operator of the parking brake, i.e., the driver, is required to judge whether the parking brake has been effectively engaged or not by a feeling in the operation of the lever, or, in other words, the intensity of the reaction force exerted by the cable to the lever. Because of this inconvenience it sometimes happens that the parking brake is not sufficiently engaged, thereby causing an accident. In fact, such an accident due to loose engagement of the parking brake often happens on a relatively moderate slope. Furthermore, in the conventional device of the abovementioned structure, since the pawl is constantly urged onto the ratchet teeth by the force of the spring, a clicking noise is generated when the lever is pivotally moved. This clicking noise is often so loud that it can awaken a baby sleeping in the passenger compartment. Therefore, some drivers who dislike the ratchet's clicking noise often operate the parking brake lever while pressing the release button.
In view of the abovementioned inconvenience, it has been proposed to remove the ratchet teeth from a portion corresponding to a small pivotal angle of the lever so that the pawl engages the ratchet teeth only when the lever has been pivotally moved beyond a predetermined pivotal angle. In this structure it is automatically effected that when the lever has been pivotally moved until the pawl engages the ratchet teeth, at least a predetermined tensile force is applied to the brake cable. However, a brake operating device of this type has a drawback in that it requires delicate adjustment and nevertheless is liable to undergo a change in adjustment as time lapses. In other words, a device which was adjusted to engage the parking brake when the lever was pivotally moved to a position where the pawl just engaged one of a few ratchet teeth will soon fail to engage the parking brake even when the lever is pivotally moved to the predetermined position, thereby causing a very serious problem with regard to the safety of the vehicle.